Excuse me, I said I can see why lollopop69 would want to pursue the matter, and I said that schools are limited in what they can do - often more limited than what they feel they would like to do.
Wrt "she's a child". That's true. But the fact this happened on school premises just isn't on. You have no choice, really (apart from Home Ed/private "choice") about sending your ds there, so they really, really have to keep him safe. You really do have the right to expect better.
Also, I have to say, this happened with my ds. Though not at school, and without serious consequences. Which points are a crucial difference. He arrived back from a playdate (aged 9) where an older brother (12) had demonstrated the flame thrower/aerosol thing. Older brother was a nice enough lad (really), as was younger brother. So, yes, some children aren't necessarily feral when they do this sort of thing.
Though, I did think "wtf", and stopped sending my ds there, pronto.
Thing is, I was able to just stop sending him around. And it wasn't at school. That's a big distinction.
So, lollipop69, I can see arguments for pursuing it. And in your shoes, I probably would.